Viscoelastic properties of [formula omitted] mixtures: comparison of guar gum with locust bean gum

Abstract

The rheological behaviour of xanthan guar gum systems has been investigated and compared to that of xanthan locust bean gum mixtures using oscillatory shear and creep-recovery measurements. The total polysaccharide concentration was kept constant at 0.5% w/w, the xanthan galactomannan ratio ranged from 1 99 to 90 10 and three ionic strengths were studied. As for xanthan locust bean gum mixtures, strong synergistic phenomena were exhibited by xanthan guar gum systems. Clearly, the addition of xanthan gum even at a very low level to a guar gum solution induced a transition of the system from a macromolecular solution to a structured system displaying gel-like properties. The comparison between three guar gum samples with different molecular weights evidenced a strong effect of the molecular weight: the higher this parameter, the stronger the synergistic interaction. At a low xanthan galactomannan ratio ( < 10 90 ), xanthan guar gum mixtures, xanthan locust bean gum mixtures (with comparable galactomannan molecular weights) resulted in similar viscoelastic behaviour. In contrast, at a higher xanthan galactomannan ratio, a stronger synergism was exhibited with locust bean gum, as expected. The rheological properties were greatly influenced by the presence of electrolyte. In the case of xanthan guar gum systems, the storage ( G′) and the loss ( G″) moduli were increased when electrolyte was present, in contrast to xanthan locust bean gum mixtures which exhibited a reverse tendency. These results provide evidence that xanthan gum plays a major role in the rheological behaviour of the xanthan galactomannan systems even at a low concentration. Overall, similar results were found with xanthan guar or xanthan locust bean gum mixtures. However, differences in the mechanism may exist according to the mannose galactose ratio of the galactomannan and also to the xanthan galactomannan ratio and the ionic strength.